Power outage without consequences: Starting the grid with decentralised plants

Project state

Started

In the future, wind turbines and photovoltaic systems as pictured here must be able to restore the grid after a failure. Photograph: soonthorn - fotolia.com

In the coming years, more and more conventional power plants will be replaced by volatile, decentralised plants such as photovoltaic systems and wind turbines. These new power plants do not provide any active reserve power to restart the grids, however. After a power outage, the current grid restoration plans will stop working. In addition, the expansion of renewable energies increases the probability of faults in general, and of major faults in particular.

In the event of a major fault, or even a complete power outage in the interconnected network, grid operators and operators of generation units have to coordinate the restoration of power supply within their own various grids. TransmissionCode 2007 governs the details of this process. Starting with the generation units, which have active and reactive power capabilities, grid restoration is about gradually re-energising the voltage-free transmission systems and distribution networks. Only then are consumers, i.e. the electrical loads, reconnected. Grid restoration is one of the five ancillary services provided by grid operators. Therefore, the actors have worked out appropriate concepts for preventive and operative measures.

Grid restoration with batteries and decentralised plants

The Kickstarter project partners are investigating new supply restoration approaches. To this end, they are examining how grid restoration by means of a stationary black start-capable large-scale battery storage system, or rather a battery power plant (BPP), would be possible in combination with a non-black start-capable combined cycle power plant and renewable energy systems. They are looking into innovative black start scenarios and grid restoration scenarios.

WEMAG operate a grid area without conventional power plants. In 2014, renewable energy plants already generated more electricity than consumers in the grid required. On balance, WEMAG already exceed the goal of the German federal government to provide 80 percent electricity from renewable energy sources by 2050. WEMAG will develop a black start and grid restoration concept that includes both BPP and the grid. For this, the engineers have to adapt the batteries, and test the black start-capability and the grid restoration in practice.

Supply restoration

If part of the grid has collapsed, for example as a result of a fault, this part must first run stably again before it can be reintegrated into the interconnected power system. Image: RWE

When restoring supply, the power plant operators and network service providers work together after an outage in order to secure power supply once again. If the network in a region collapses, it is disconnected from the grid. The power plants then form a network to which successively more loads are connected. The network is only switched on when it is running stably and is synchronised with the interconnected power system. In contrast to the conventional top-down approach, it will also be possible to expand future energy networks from below – i.e. from the low- and medium-voltage range up to the high and extra-high voltage level.

In the adjacent grid area of Schwerin, the energy supply of Schwerin has two combined cycle power plants with upstream biogas combined heat and power plants (CHP), which have limited black-start capabilities. Therefore, they are not yet included in a grid restoration concept. The project partners aim to change this and modify the plants to make them suitable for black starts. These changes will be then tested in practice.

Schematic illustration of the project structure of Kickstarter. Graphic: Younicos

Together with WEMAG, the company Younicos have built a 5-MW battery storage system in Schwerin, and they operate a technology centre with battery storages in the megawatt range. In close cooperation with WEMAG, Younicos will develop the black start and grid restoration concept, and model and toughen up the necessary BPP and field test it.

The University of Rostock has developed the grid restoration concept for the control area of 50Hertz Transmission, and has prior experience in this area. Furthermore, the university is highly experienced in terms of grid conditions due to various grid studies. Within the project, the University of Rostock will create a grid model with dynamic power plant models, identify grid expansion scenarios and develop a grid restoration concept. The university will also prepare and evaluate the test.